The field of the disclosure relates generally to power transmission systems and pipeline heating systems, and, more specifically, to a combined DC power transmission and heating system that transmits DC power to a load and provides direct electric heating to a pipeline.
Most land based electrical power transmission systems transmit high-voltage alternating current (AC) power from an electrical power source, such as a generator, to an electrical load, such as a motor. AC power transmission systems are more prevalent than DC transmission systems due to the reduced cost, and improved efficiency, of AC transformers and switchgear in generating high-voltage power. High-voltage power is transmitted through transmission cables with reduced power losses compared to low-voltage power. Accordingly, any conversion to low-voltage AC and/or DC power is typically performed as close to the electrical load as possible. However, AC power transmission systems have reactive power losses associated with the transmission cables that do not exist in DC transmission systems. As such, DC power transmission systems are more efficient and cost effective when transmitting power over long distances where the reactive losses outweigh the more expensive DC transformer equipment. This is especially true in undersea cables, where the reactive power losses are increased due to large charging currents. Accordingly, one application of DC power transmission systems is providing power to motors that operate gas compressors, pumps, and/or other fluid transportation devices that channel a fluid, such as crude oil, through a pipeline to a surface infrastructure for processing and refinement. The motors are typically located remotely from the surface infrastructure, for example, proximate undersea or subterranean oil deposits.
To facilitate the transportation of fluid through the pipeline, some known fluid transportation operations use electric pipeline heating systems to provide direct electric heating to the pipeline. More specifically, in known electric pipeline heating systems, a stand-alone AC or DC power system provides electrical current through electrical conductors coupled to the pipeline, or through the pipeline itself, to generate heat via resistive current losses, referred to as the Joule effect. The electrical conductors conduct the generated heat to the fluid within the pipeline to facilitate reducing the overall viscosity of the fluid and to facilitate improving efficiency of the motors. Heated pipelines prevent the buildup of solid materials in the pipeline and facilitate continuous flow throughout the pipeline, even when the fluid circulates underwater.
However, known electric pipeline heating systems and known power transmission systems are stand-alone systems. Specifically, both systems require separate electrical power sources and separate transmission cables to operate. In particular, known electric pipeline heating systems must maintain fluid temperature during shutdowns, be capable of supporting high currents to heat long pipelines, be capable of heating the fluid within a specified time period, and be capable of continuous heating of the pipeline. To meet these requirements, current electric pipeline heating systems require a power supply and a transmission cable that are independent of the electrical loads of the power transmission system. In addition, DC power transmission systems selectively disable at least a portion of the electrical load, for example, during maintenance during which the pipeline must still be heated. Separate DC power transmission systems and separate electric pipeline heating systems increase the capital costs associated with known fluid transportation operations.